HTTP 503 is a status code that indicates a server is temporarily unable to handle a request. This can happen for various reasons, such as server overload, maintenance, or unexpected issues. When a user encounters this error, it means the server is currently unavailable but may be back online shortly. When a server returns an HTTP 503 response, it often includes a "Retry-After" header. This header informs the client how long to wait before trying the request again. Users may see a message indicating that the service is unavailable, prompting them to check back later.